The present invention relates to a hydraulic control device for a primary hydraulic consumer and a secondary hydraulic consumer.
A hydraulic control circuit of this type is known, e.g., from DE 197 03 997 A1. The pressure medium flows to the two hydraulic consumers via metering orifices. A pressure scale is located upstream of the first metering orifice, which is assigned to the primary, first hydraulic consumer, and a pressure scale is located downstream of the second metering orifice, which is assigned to the secondary, second hydraulic consumer. The pressure scales serve to maintain constant pressure differences via the metering orifices when the quantity of pressure medium delivered is sufficient, independently of the load pressures. As a result, the quantity of pressure medium flowing to a hydraulic consumer depends only on the opening area of the particular metering orifice. The pressure medium source is typically an adjustable hydropump that is controllable as a function of the highest load pressure such that the pressure in a supply line is greater than the highest load pressure, by a certain pressure difference.
With regard for the first consumer, the control circuit corresponds to a load-sensing control (LS control). LS control or LS consumers are typically referred to when hydraulic consumers are controlled to which pressure medium flows via a meter orifice and an upstream pressure scale, and when the pressure scale registers the falling pressure via the particular metering orifice and holds it constant. The pressure scale is acted upon in the closing direction only by the pressure in front of the metering orifice, and it is acted upon in the opening direction only by the load pressure of the particular hydraulic consumer and by a compression spring.
With regard for the second consumer, the control circuit corresponds to an LUDV control. In this case, the pressure scale located downstream of the second metering orifice is acted upon in the opening direction by the pressure after the second metering orifice, and it is acted upon in the closing direction by a control pressure that is present in a rear control space, the control pressure typically corresponding to the highest load pressure of all hydraulic consumers supplied by the same hydropump. If several hydraulic consumers controlled in this manner are actuated simultaneously, the quantities of pressure medium flowing to them are reduced by the same ratio when the quantity of pressure medium delivered by the hydropump is less than the partial quantities of pressure medium demanded. This case is referred to as a control with load-independent flow distribution (LUDV control). The hydraulic consumers controlled in this manner are referred to as LUDV consumers. LUDV control is a special case of load-sensing control (LS control). In that case as well, the highest load pressure is also sensed, and the pressure medium source generates an inlet pressure that is greater than the highest load pressure by a certain amount Δp.
Publication DE 197 03 997 A1 mentioned above discloses a priority-based switching between the LS consumer and one or more LUDV consumers, in which priority is given to supplying the LS consumers with pressure medium. In addition to the pressure scale of the LS consumer, a priority valve is provided that includes a first connection, which is connected with a line section upstream of the first metering orifice and a second connection connected with the load-sensing line, and the valve element of which is capable of being acted upon—in the direction in which the connection between the first connection and the second connection is opened—by the load pressure of the primary hydraulic consumer, i.e., the LS consumer, and by an additional force. In the closing direction, the valve element is acted upon by pressure upstream of the metering orifice of the LS consumer—in a supply line or between the pressure scale and the first metering orifice. In this manner, it is ensured that priority is given to supplying the LS consumer with pressure medium. In particular, the pressure upstream of the first metering orifice is regulated to a value that is higher than the load pressure of the primary consumer at least by an amount that corresponds to the additional force that acts on the valve element of the primary valve.